Bowstrings serve an important role in the shooting of a bow. Sometimes, bowstrings break before their life expectancy. Other times, bowstrings lose elasticity, resulting in a slack that hinders shooting performance. Fibers for use in strands of bowstrings of bows and crossbows experience challenges that are not experienced by fibers in other fields. For example, a bowstring may be formed through a manufacturing tensioning process. In the manufacturing tensioning process, the manufacturer tensions a plurality of individual strands, each strand including a plurality of fibers, to a predetermined manufacturing tension (e.g. 600 lbs of force). While under the predetermined manufacturing tension, the plurality of individual strands may then be twisted at a predetermined pitch (e.g. one twist for every 1.25 inches of length). Servings, such as wax and/or dye, may be applied while under the predetermined manufacturing tension. As a result of tensioning the strands at the pre-determined manufacturing tension during the twisting process, the individual strands settle or set into a twisted state. This setting or settling helps to prevent the bowstring from creeping and elongating after the manufacturing tensioning process, such as during use of the bowstring in a bow.
A number of materials are used in the formation of bowstrings, such asultra high molecular weight polyolefins. Ultra high molecular weight polyolefins are polyolefins that have a molecular weight greater than about one million and often between three million and six million. Examples of ultra high molecular weight polyolefin fibers include the fibers sold under the tradenames SPECTRA® and DYNEEMA®. Bowstrings formed from SPECTRA® 1000 experience undesirable creep (the tendency to stretch under tension without return when the tension is removed, resulting in slack) when tensioned in a bow or crossbow. Undesirable creep can occur during use of the bowstring. For example, the bowstring may have an initial length when under an initial installation tension as installed on a bow. When the archer draws back the bowstring, applying a drawback tension, the bowstring stretches to a drawback length that is much greater than the initial length. When the archer releases the bowstring and the drawback tension, the bowstring shortens to a return length. Due to creep, the return length can be substantially greater than the initial length, resulting in undesirable slack in the bowstring. This slack can hinder shooting performance and accuracy.
Bowstrings formed from DYNEEMA® experience high elasticity (the tendency to stretch under tension and then return when the tension is removed), but the return action can be counterproductive to the manufacturing tensioning and setting process described above. Bowstrings with high elasticity have been found to be unsuitable with the manufacturing tensioning and setting process described above—the bowstrings return to their original states too readily, and the setting process fails during or upon completion of the manufacturing tensioning process. Issues such as elasticity and elongation are particularly pertinent to bowstrings that have servings applied while the bowstring was under the predetermined tension. In these bowstrings, servings tend to separate or deteriorate when the bowstrings elongate after returning to their original states. For example, lower grade DYNEEMA® will elongate through the pre-stretching manufacturing process, but may also be subject to future elongation and does not have the same feel and stability of the material with the higher grade DYNEEMA®. When higher grade DYNEEMA® is used, the elasticity levels are greater (creating stability and superior feel) but, due to this elasticity, the pre-stretching manufacturing process causes the bowstring to take a temporary set, resulting in a finite amount of “return.” For example, a bowstring may be pre-tensioned to have a finished length of fifty-eight inches after finishing (hot length). This is a standard measurement used in the archery industry where the measurement is taken at 100 lbs of tension measure on one-quarter dowel pins. Once this bowstring has sat for several hours, the finished length may decrease and return anywhere from one-quarter to one-eighth inch due to the elasticity. Combining DYNEEMA® with VECTRAN® can still result in an undesirable decrease and return of one-sixteenth to one-eighth inch of change.
Materials used in the formation of bowstrings also include liquid crystal polymer fibers. Examples of liquid crystal polymer fibers include the fibers sold under the tradename VECTRAN®. Bowstrings formed from VECTRAN® are prone to break during use. Such bowstrings are also unsuitable with the manufacturing tensioning and setting process described above. The servings of such bowstrings tend to separate or deteriorate after the bowstrings return to their original states.
Some bowstrings have been formed from a blend of ultra high molecular weight polyolefin fibers and liquid crystal polymer fibers (e.g. 10-30% liquid crystal polymer fibers and 70-90% ultra high molecular weight polyolefin fibers). While bowstrings formed from such a blend experience improved creep and reduced tendency to break, they have still been found to be unsuitable for use with the manufacturing tensioning and setting process described above. The servings of such bowstrings tend to separate or deteriorate after the bowstrings return to their original states.
Materials used in the formation of bowstrings also include blends of ultra high molecular weight polyolefin fibers and stretched polytetrafluoroethylene fibers. Examples of stretched polytetrafluoroethylene fibers include the fibers sold under the tradename GORE-TEX®. While bowstrings formed from such a blend experience improved creep and reduced tendency to break, they have still been found to be unsuitable for use with the manufacturing tensioning and setting process described above. The servings of such bowstrings tend to separate or deteriorate after the bowstrings return to their original states.
The foregoing background describes some, but not necessarily all, of the problems, disadvantages and shortcomings related to compositions, structures, and manufacture of bowstrings.